An out-of-balance driveline in a vehicle can cause a driveshaft, extending from the transmission to the axle to experience once per driveshaft revolution excitations. Driveline components inherently posses slight out-of-balance characteristics. Unfortunately, the driveshaft excitations create unwanted noise and vibration in the vehicle passenger compartment. To improve the vehicle tactile and audible characteristics (i.e., reduce the noise and vibration to acceptable levels) resulting from these excitations, a balancing of the vehicle driveline or its elements is needed.
Current automotive assembly lines typically do not make corrections for overall imbalances of the driveline after assembly of the vehicle. Typically, the individual components, or, at most, a pair of adjacent components of a driveline, are balanced prior to assembly into the vehicle. Several techniques are currently employed for balancing individual vehicle driveshafts and other driveline components while mounted in fixtures or balancing machines. However, the end constraints (i.e., the boundary conditions) on the driveshafts and other components will change when they are removed from the fixtures and assembled into a vehicle.
Although every effort is made to minimize the imbalance of each component separately, each will still posses small residual imbalances. Consequently, once the individual components are assembled into vehicles, there still exists the potential for addition of these small residual imbalances, which may, in total, exceed acceptable overall limits of imbalance for the particular vehicle design.
The need arises, then, for an overall balancing system that can detect out of balance drivelines after assembly into a vehicle and determine the correction needed to reduce the imbalance to an acceptable value.
Currently, equipment is available to do balancing of rotating objects, and has been used in the aerospace industry, but it would require three runs on rollers of a chassis dynamometer to accomplish the balancing of an automotive vehicle driveline. Requiring three runs adds to the time and cost of balancing a vehicle driveline, making it an expensive procedure if one desires to test each vehicle coming off of an assembly line.
The known system involves rotating a shaft at a predetermined speed, measuring the acceleration and calculating the resultant imbalance at each end of the shaft. Then, a trial weight is added near a first end of the shaft and the shaft is again rotated at the predetermined speed, again the acceleration is measured and the resultant imbalance is calculated at each end. And then, the trial weight at the first end is removed and a trial weight is added near the second end of the shaft. The shaft is rotated at the predetermined speed, and the acceleration is measured and the resultant imbalance is calculated at each end. The data are then fed into an analyzer which compares the imbalances for each of the three runs and determines influence coefficients by employing a computer program. From the influence coefficients, the amount of weight needed to be added to the first and second ends of the shaft in order to balance it can be determined. However, as stated earlier, this requires the addition and removal of trial weights as well as rotation of the shaft three separate times for each vehicle tested. This process would be time consuming and expensive to conduct for a substantial number of vehicles coming off of an assembly line, thus making it impractical.
In order to minimize the cost of balancing vehicle drivelines for substantially every assembled vehicle coming off of an assembly line, a balancing process needs to be as brief as possible. It should be brief because a significant number of the vehicles will have drivelines that are sufficiently in balance and will not need to have weights added to balance them. Also, the test needs to be non-destructive, since the vehicles are assembled and essentially ready for delivery.
The need exists, then, for an inexpensive, simple, fast and accurate method and system for balancing drivelines that will assure that vehicles in which the components, although they may be balanced individually before assembly, will be balanced and those that posses acceptable levels of overall imbalances after assembly into a vehicle do not have unnecessary balancing operations performed on them.